Hot gas defrost system including bypass-suction line heat exchange



July 21, 1959 B. B. LATTER 2 895,3

HOT GAS DEFROST SYSTEM INCLUDING BYPASS-SUCTION LINE HEAT EXCHANGE FiledFeb. 27, 1957 INVENTOR. BRucE s. LATTEP- His A'i'ToRuW-Y United StatesPatent Ofiice 2,895,306 Patented July 21, 1959 HOT GAS 'DEFROST SYSTEMINCLUDING BYPASS- SUCTION LINE HEAT EXCHANGE Bruce B. Latter,Louisville, Ky., assignor to General Electric Company, a corporation ofNew York Application February 27, 1957, Serial No. 642,823

2 Claims. (Cl. 62-152) The present invention relates to a refrigeratingsystem including means for the hot gas defrosting of a low temperaturecompartment evaporator component of the system. It is more particularlyconcerned with a twotemperature refrigerating system including a lowtemperature compartment evaporator and a high temperature compartmentevaporator in series connection in the system and improved means for thehot gas defrosting of the low temperature compartment evaporator.

Household refrigerators of the two-temperature type normally include afirst evaporator which operates continuously at below-freezingtemperatures for the storage of frozen foods and a second evaporator formaintaining the fresh food compartment of the refrigerator at abovefreezing temperatures. Because the accumulation of frost on evaporatorsurfaces lowers the etficiency of the refrigerating system, it isnecessary periodically to remove the frost accumulation. Since thetemperature of the fresh food compartment is above freezing, the removalof frost from the evaporator serving the compartment presents noparticular problem. For example, the evaporator used to cool thatcompartment can be operated above freezing during part of therefrigerating cycle, thus permitting the accumulated frost to melt.However, since the freezer compartment must be held continuously attemperatures well below freezing for the proper storage of frozen foodand since that evaporator is normally in contact with or closelyadjacent to at least part of the contents of the freezer compartment,any acceptable automat-i defrosting arrangement for the freezerevaporator must not only effect rapid melting of the accumulated frostbut must also accomplish this melting at the lowest possibletemperature.

It is an object of the present invention to provide an automatic hot gasdefrosting system for defrosting a freezer evaporator both rapidly andat temperatures close to freezing temperatures.

A more specific object of the invention is to provide a hot gas defrostsystem by means of which the compressed refrigerant gas is introducedinto the evaporator at a temperature such that only the latent heat ofthe refrigerant is employed for defrosting purposes.

Further objects and advantages of the invention will become apparent asthe following description proceeds, and the features of novelty whichcharacterize the invention 'will be pointed out with particularity inthe claims annexed to and forming a part of this specification.

In carrying out the objects of the invention, there is provided arefrigerating system comprising a compressor, a condenser, a capillarytube flow restricting element, evaporator means including a lowtemperature or freezer evaporator, and a suction line connected inseries refrigerating circuit. During normal operation of this systemcompressed refrigerant from the compressor is condensed in the condenserand passes through a capillary tube to the evaporator means Where it isevaporated for maintaining the proper refrigerating temperatures withina refrigerator. Vaporized refrigerant is returned through the suctionline to the compressor. In accordance with the usual practice, thesuction line and capillary tube are arranged in heat exchangerelationship for reasons which are well known in the art. The systemalso includes a defrosting comprising conduit connecting the compressordirectly to the inlet end of the freezer evaporator for in troducing hotcompressed refrigerant directly from the compressor into the evaporator.In accordance with the present invention this conduit is arranged inheat exchange relationship with the suction line so that the cool gas inthe suction line will remove from the hot compressed refrigerantsubstantially all of the superheat with the result that the defrostinggas as introduced into the freezer evaporator will be only slightlyabove its condensing temperature. Melting of the accumulated frost onthe freezer evaporator is then accomplished by the latent heat given upby the defrosting gas. As a result the accumulated frost is removed fromthe freezer evaporator at the lowest possible temperatures. In additionthe heat interchange between the bypass conduit and the suction linewarms the suction line to prevent undesirable sweating thereof underhumid ambient conditions. This warming of the suction line and hence thesuction gas also serves to increase the load on the compressor. Also byoperating the bypass conduit at temperatures somewhat lower than thosewhich would exist without the heat exchange arrangement, heat losses toambient between the compressor and the freezer evaporator are minimizedor decreased.

For a better understanding of the invention reference may be had to theaccompanying drawing in which:

Fig. 1 is a view of a'portion of a refrigerator incorporating anembodiment of the present invention; and

Fig. 2 is a schematic illustration of a refrigerating sys tem employedin the refrigerator of Fig. 1.

Referring to the drawing there is shown in Fig. 1 a portion of atwo-temperature refrigerator which includes a frozen food compartment 1and a fresh food compartment 2. The refrigerating system employed tomaintain these two compartments at their proper operating temperaturesis shown schematically in Fig. 2. This system includes a hermeticallysealed motor-compressor unit 3 and a condenser 4. The system furtherincludes a low temperature or freezer evaporator 5 which is disposed inheat exchange relationship with the walls of the freezer compartment 1and a fresh food evaporator 6 which is disposed in the fresh foodstorage compartment 2 and is designed to maintain this compartment atabove freezing temperatures. During the normal refrigerating cycle,compressed refrigerant is supplied from the compressor 3 to thecondenser 4. In the condenser 4 the hot com- -pressed refrigerant iscooled and liquified and passes through a capillary tube 8 into thefreezer evaporator S which is arranged in the form of a serpentine coilalong the top, back and side walls of the freezer compartment 1. Fromthe freezer evaporator 5, the refrigerant passes through a loop 9extending upwardly along the back wall of the freezer compartment 1 andthen downwardly into the serpentine fresh food evaporator 6 arranged inthe storage compartment 2. In these two evaporators liquid refrigerantis vaporized and the refrigerant vapor collecting in header 10 connectedto the outlet end of the serpentine evaporator 6 is returned through thesuction line 11 to the compressor 3. Preferably, the suction line 11 isin heat exchange relationship with the capillary 8 so that the coolrefrigerant vapor in the suction line will further cool the refrigerantliquid passing to the evaporator system through the capillary 8. Inaddition the heat exchange between the capillary 8 and the suctionline'11 tends to raise the temperature of the gas in the suction line 11to maintain the portions of the line such as the portion 12 exposed toambient conditions above the dew point and thus prevent sweating of thesuction line.

The normal operation of the system 1s controlled by the switch 15 whichis adapted to engage the contacts 16.

in a line 17 through which power is supplied to the motor compressorunit3. The switch 15 is actuated by a bellows 18 in response to thetemperature of the fresh food evaporator 6 by means of the thermostaticbulb 19 positioned in contact with the evaporator 6. Accordingly, thenormal or refrigerating operation of the system is controlled by thetemperature of the fresh food evaporator 6. To preventthe accumulationof frost on the evaporator, the switch 15 is arranged to energize thecompressor unit 3 only after the fresh food evaporator 6 has attained atemperature above freezing .to assure the melting of accumulated frostcollecting on this evaporator during the previous cycle of operation ofthe compressor and to de-energize the compressor unit 3 when the freshfood evaporator 6 has reached a sub-freezing temperature in theneighborhood of or close to that sought to be maintained in the freezercompartment 1.

Due to the fact that the freezer compartment 1 is separate from andinsulated from the fresh food compartment 2, the temperature of thefreezer compartment will fluctuate only a few degrees during the on andoff cycles of the compressor unit 3 even though the evaporator 6subjected to the higher temperatures of the fresh food compartment 2will exhibit a temperature change over a range from approximately F. to35-37 F.

Because the freezer evaporator operates continuously at well belowfreezing temperatures, there is a gradual accumulation of frost withinthe freezer compartment 1 and more specifically on the walls fromingthis compartment. reducing the etficiency of the freezer evaporator, itis necessary to remove the accumulated frost from time to time.Furthermore, since this frost must be removed in a manner which will notcause a substantial rise in the temperature of the frozen foods storedin that compartment, the means for hot gas defrosting of the freezerevaporator 5 provided in accordance with the present inventionisdesigned .to eifect the periodic removal of frost from his evaporatorboth rapidly and at relatively low temperatures. To accomplish thesepurposes there is provided a conduit 21 bypassing the condenser 6 andthe capillary 8 and connecting the outlet of the compressor 3 to theinlet portion 22 of the freezer evaporator 5. A solenoid valve 23provided at the junction of the bypass line 21 with the line 24connecting the compressor 3 with the condenser 4 is provided to controlofthe flow of refrigerant through the bypass line 21.

When the solenoid valve 23 is de-energized the refrigerant follows thenormal path from the compressor 3-to the condenser 4. Energization ofthe valve 23 causes the refrigerantto flow through the bypass line 21directly to the frozen food evaporator 5.

The operation of the valve 23 is controlled by a switch 26 which alsocontrols the operation of the compressor 3 independent of the switch 15.The switch 26 may be of any suitable type. For example, it may be amanually controlled switch whereby the user of the refrigerator.

against which the compressor unit 5 must pump and there by increase thewatt input to the compressor inptor sub- As this layer of frost has aninsulating effect stantially abovethe input in the case where anonrestricted hot gas flow line is employed.

During operation of the system of this type on the defrost cycle,compressed gaseous refrigerant flows from the bypass line 21 through thefreezer evaporator 5 and raises the temperature of this evaporator tothat which will effect melting of accumulated frost. In order to limitthe temperature rise of any portion of the freezer refrigerant enteringthe freezer evaporator 5 is at a temperature such that substantiallyonly the latent heat of the compressed refrigerant is employed fordefrosting purposes. By thus removing the superheat from the compresseddefrosting refrigerant gas and using only the latent heat, defrosting ofthe freezer evaporator is accomplished at the lowest possibletemperature, and with the least possible temperature gradient fromevaporator inlet to outlet. In other words by removing the superheatthrough heat exchange of the suction line 12 and the bypass line 21local hot spots and hence local thawing of the contents of the freezercompartment 1 which may result when superheated refrigerant gas ispassed directly to the freezer evaporator 5 are avoided.

It will be obvious of course that the heat exchange arrangement of thebypass line 21 and the suction line 12 is preferably designed so thatall of the superheat is removed from the bypass refrigerant gas and thegas enters the freezer evaporator 5 at approximately its condensingtemperature. The heat liberated by condensation of the compressedrefrigerant in the freezer evaporator 5 quickly effects melting of thefrost accumulated on this evaporator and on the walls of the compartmentonly while the freezer evaporator is at a temperature colder than thefresh food compartment air. The liquid refrigerant which may flowfromthe fresh food evaporator 6 through the header 10 and into the suctionline 12 connecting the header 10 to the compressor 3 during the defrostcycle will be evaporated by the heat exchange of the suction line 12which the bypass line 21 thereby avoiding the introduction of liquidrefrigerant into the compressor 3.

Since the portions 32 of the suction line 12 adjacent the compressorunit 3 are normally subjected to ambient conditions, heat interchangebetween the suction line 12 and the bypass line 21 is preferablyarranged to maintain these portions of the suction line. at temperaturesabove the dew point thereby preventing any undesired sweating of thesuction line during the defrosting operation.

From the above description it will be seen that the present inventionprovides means for effecting defrosting of the freezer evaporator at lowand safe temperatures. Also by the arrangement for heat exchanging thesuction line and the bypass line those portions of the suction lineexposed to ambient conditions are maintained well above the dew pointthereby eliminating any sweating problem of the suction line.Furthermore, since all of the heat given up by the bypass line to thesuction line is carried by the suction gas through the compressor andback to the bypass line and hence to the freezer evaporator 5, this heatis not lost and is therefore available for defrosting purposes. Inaddition since the heat exchange between the bypass line 21 and thesuction line 12 at a point close to'the compressor unit 3 lowers thetemperature of the hot compressed refrigerant passing through the bypassline 21 heat losses of the system during the defrost cycle in the formof radiation and convection losses from the bypass line arecorrespondingly reduced.

While there has been shown and described a specific embodiment of thepresent invention, it is not desired that the invention be limited tothe particular construction shown and described. For example, theinvention is: not limited to the application to the defrosting of thefreezer evaporator of the two-temperature refrigerator but can beapplied equally Well to the defrosting of the evaporator means for afood freezer.

What I claim as new and desire tosecure by Letters Patent of the UnitedStates is:

1. A refrigerating system comprising a compressor, a condenser, acapillary tube flow restricting element, a freezer evaporator forcooling a frozen food compartment, a fresh food evaporator formaintaining a fresh food compartment at above-freezing temperatures anda suction line, said compressor, condenser, capillary tube element,freezer evaporator, fresh food evaporator and suction line beingconnected in series in a closed refrigcrating circuit, a portion of saidsuction line being in heat exchange relationship with said capillarytube flow restricting element, control means responsive tothetemperature of said fresh food evaporator for starting said compressoronly when said fresh food evaporator has attained a temperature abovefreezing to assure defrosting of said fresh food evaporator prior toenergization of said compressor and means for periodically defrostingsaid freezer evaporator including a conduit bypassing said condenser andflow restricting element and connecting said compressor directly to theinlet to said freezer evaporator for the introduction of hot gas intosaid freezer evaporator, a valve in said conduit controlling the flow ofrefrigerant therethrough, control means for controlling the operation ofsaid valve and energizing said compressor when said valve is open, saidbypass conduit being in heat exchange contact with a part of saidsuction line adjacent said compressor and between said portion of saidsuction line in heat exchange relationship with said capillary tube flowrestricting element and said compressor thereby to remove from the hotcompressed gas entering said freezer evaporator during defrostingoperation of the system substantially all of the superheat wherebydefrosting of the freezer evaporator is effected substari tially by thelatent heat of the compressed gas.

2. A refrigerating system comprisinga compressor, a condenser, acapillary tube flow restricting element, a freezer evaporator forcooling a frozen food compartment, a fresh food evaporator formaintaining a fresh food compartment at above-freezing temperatures anda suction line, said compressor, condenser, capillary tube element,freezer evaporator, fresh food evaporator and suction line beingconnected in series in a closed refrigerating circuit, control meansresponsive to the temperature of said fresh food evaporator for startingsaid compressor only when said fresh food evaporator has. attained atemperature above freezing to assure defrosting of said fresh foodevaporator prior to energization of said compressor and means forperiodically defrosting said freezer evaporator including a conduitbypassing said condenser and flow restricting element and connectingsaid compressor directly to the inlet to said freezer evaporator for theintroduction of hot gas into said freezer evaporator, a valve in saidconduit controlling the flow of refrigerant therethrough, control meansfor controlling the operation of said valve and energizing saidcompressor when said valve is open, said bypass conduit being in heatexchange contact with said suction line adjacent said compressor therebyto cool the hot compressed gas entering said freezer evaporator duringdefrosting operation of the system to a temperature such that defrostingof the freezer evaporator is effected substantially only by the latentheat of the compressed gas.

References Cited in the file of this patent UNITED STATES PATENTS2,526,379 Maseritz Oct. 17, 1950 2,694,904 Lange Nov. 23, 1954 2,694,906Didion Nov. 23, 1954 2,698,521 Mann Jan. 4, 1955 2,783,621 Staebler Mar.5, 1957 2,801,523 Hansen Aug. 6, 1957 2,807,149 Williams Sept. 24, 1957

